The present invention generally relates to ignition systems for gasoline engines. More particularly, the invention relates to a discharge ignition apparatus that provides automatic spark advance at predetermined operating speeds.
Ignition circuits of relatively elaborate design have often been provided to advance the ignition spark as engine speed is increased. For example, the spark may be delayed at starting speeds until approximately peak compression of the engine""s piston. At higher engine speeds, the spark is preferably advanced to occur before peak compression. For example, it may be desirable in many applications to have an advance of about fifteen (15) mechanical degrees.
In one aspect, the present invention provides an ignition apparatus for use with an internal combustion engine to produce an electrical spark at a spark ignition device. The apparatus comprises a magnet assembly, including a pair of pole faces, operatively revolved along a circular path. A magnetically permeable core is mounted adjacent to the circular path and has at least two leg portions each including a respective end face. The leg portions of the magnetically permeable core are situated such that the pole faces pass proximate to the end faces during revolution of the magnet assembly. As a result, a time-varying magnetic flux is produced in the magnetically permeable core.
The ignition apparatus further includes a transformer having a primary coil and a secondary coil related by a predetermined step-up ratio. The secondary coil is electrically connected during operation to the spark ignition device. A spark generation circuit is operative to apply a primary voltage pulse to the primary coil responsive to a triggering signal. The primary voltage pulse produces a spark generating pulse in the secondary coil.
In addition, the ignition apparatus includes triggering circuitry electrically connected to the primary coil to produce the triggering signal based on a voltage induced in the primary coil by revolution of the magnet assembly. The triggering circuitry is adapted so as to automatically produce advancement of the triggering signal at predetermined operating speeds.
In some exemplary embodiments, the ignition apparatus comprises an energy storage element such as a charge capacitor. A charge coil has a voltage induced thereon by the magnetic flux to supply charging energy to the energy storage element during each revolution of the magnet assembly. An electronic switch, such as an SCR, is electrically connected in circuit with the energy storage element and the primary coil. The electronic switch is rendered conductive by application of the triggering signal thereto. Often, it will be desirable to locate the transformer and the charge coil on different leg portions of the magnetically permeable core.
The triggering circuitry may preferably comprise a peak detect circuit operative to indirectly produce the triggering signal from voltage induced in the primary coil when the triggering signal is not advanced. When the triggering signal is advanced, connection circuitry are operative to directly produce the triggering signal from voltage induced in the primary coil. For example, the triggering circuitry may be adapted such that the triggering signal is produced on a trailing edge of a predetermined half cycle of the primary coil induced voltage when not advanced and is produced on a leading edge of the half cycle when advanced.
The peak detect circuit may be configured having a diode electrically connected to a holding capacitor. In such embodiments, the holding capacitor may be selectively discharged by a trigger switch so as to produce the triggering signal. Often, the trigger switch may a transistor (such as a PNP bipolar transistor).
In presently preferred embodiments, the ignition apparatus may be configured so that the triggering signal will advance by at least about 10 degrees. For example, the triggering signal may preferably advance by about 14-15 degrees in some exemplary embodiments. Moreover, it will often be desirable if the triggering signal when advanced occurs at a time when a spark sustaining potential is being otherwise induced on the secondary coil.
In other aspects, the present invention provides a discharge circuit for use in a discharge ignition system of the type operative to produce an electrical spark at a spark ignition device. The discharge circuit comprises a charge capacitor, a charge coil and a rectifier electrically connected between the charge coil and the charge capacitor. A transformer is also provided, including a primary coil and a secondary coil. The secondary coil is electrically connected during operation to the spark ignition device to produce the electrical spark.
The discharge circuit further includes an electronic switch electrically connected in circuit with the charge capacitor and the primary coil. The electronic switch is rendered conductive by a triggering signal applied to a triggering node thereof. Toward this end, triggering circuitry is electrically connected to the triggering node. The triggering circuitry is operative to produce the triggering signal based on a voltage induced in the primary coil. Moreover, the triggering circuitry is adapted so as to automatically produce advancement of the triggering signal at predetermined operating speeds.
Additional aspects of the present invention are provided by a discharge ignition apparatus for use with an internal combustion engine to produce an electrical spark at a spark ignition device. The apparatus comprises a movable magnet assembly including a pair of pole faces. A magnetically permeable core is provided, having at least two leg portions each including a respective end face. The magnetically permeable core is mounted such that the pole faces pass proximate to the end faces as the magnet assembly is operatively moved in a cyclical manner to produce a time-varying magnetic flux in the magnetically permeable core. A housing is mounted to at least one of the leg portions of the magnetically permeable core. A transformer having a primary coil and a secondary coil is located in the housing and situated about the magnetically permeable core. The secondary coil of the transformer is electrically connected during operation to the spark ignition device.
The discharge ignition apparatus further comprises a discharge circuit located in the housing. The discharge circuit includes a charge coil situated about the magnetically permeable core to have a charging voltage induced thereon by the magnetic flux. As a result, charging energy is supplied to an energy storage element.
An electronic switch is electrically connected in circuit with the energy storage element and the primary coil. Activation of the electronic switch during operation produces a voltage on the primary coil. Toward this end, triggering circuitry is provided which is operative to activate the electronic switch at a first triggering point when the engine is operating at speeds below a predetermined threshold. When the engine is operating at speeds above the predetermined threshold, the triggering circuitry is operative to activate the electronic switch at a second triggering point. The second triggering point is advanced with respect to the first triggering point and occurs at a time when a spark sustaining potential is being otherwise induced on the secondary coil.
Other objects, features and aspects of the present invention are discussed in greater detail below.